The combination of retinoids and antibiotics is of great interest in dermatology, due to the established synergistic efficacy of the two actives in treating acne. Retinoids are powerful keratolytic agents and antibiotics provide anti-bacterial activity for treating acne. Antibiotics such as erythromycin and clindamycin are soluble in aqueous media. Retinoids are insoluble in water. When formulating combination actives for treating acne, it is important to keep the retinoids in complete solution as well as antibiotics in solution. For example, aqueous retinoid acid formulations containing no alcohol and no fats have not shown to be clinically efficacious because the active ingredients are not dissolved in solution, and therefore not available for effectively treating the skin. See, U.S. Pat. No. 5,690,923.
Unfortunately, retinoids alone in formulations have been known to be quite unstable. The stabilization of retinoids by dissolving in alcohols has been proposed. For example, U.S. Pat. No. 5,721,275 discloses a topical composition containing a retinoid as a single active ingredient wherein in large concentrations of alcohol are used to dissolve the retinoids in solution. However, the stability of the composition containing high levels of alcohol is limited and high levels of alcohol will irritate the skin. Retinoids have also been formulated in aqueous vehicles using surfactants. For example, U.S. Pat. No. 5,690,923 discloses the use of surfactants such as ethoxylated alcohol, ethers, and block polymers to solubilize retinoids in water without using any alcohol.
There exists room for improvement in the area of formulating, packaging, storing and dispensing compositions containing both retinoids and antibiotics to satisfactorily provide a full two year expiration date. Specifically, a need exists for a composition containing a retinoid and an antibiotic in complete solution, in which both active are chemically and physically stable.